Control system



Apfil 28, 1942. w. G. COOK CONTROL SYSTEM Filed Nov. 29, 1939 2Sheets-Sheet l ti Q INVENTOR 1 ///0/'a G. 600K.

WITNESSES:

: It! ATTORNEY April 28, 1942. w. e. COOK 2,281,063

CONTROL SYSTEM Filed Nov. 29, 1939 2 Sheets-Sheet 2 WITNESSES: INVENTORMWO/"O G 60 OK, fi I Patented Apr. 28, 1942 UNITED STATES PATENT OFFICECONTROL SYSTEM Willard G. Cook, Wilkinsburg, Pa., assignor toWestinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., acorporation of Pennsylvania 13 Claims.

This invention relates, generally, to control systems, and, moreparticularly, to systems for controlling the tension on strip materialas it is being passed through a rolling mill.

In the operation of steel strip rolling mills it is desirable that backand front tensions be applied to the strip as it enters and leaves theworking rolls. In some instances it is highly desirable to maintainfront and back tensions on the strip of greater magnitude than can beapplied through the winding and unwinding reels. It has become thepractice, therefore, to provide tensioning devices between the unwindingreel and the working rolls and between the working rolls and the windingreel which will function to provide much higher front and back tensionsat the working rolls than the winding and unwinding reel tensions. Onesuch tensioning device for providing front tension on the strip as itleaves the roll stand has been in the form of a pulling devicecomprising a pair of driven rolls over which a partial wrap of the stripis taken in passing from the roll stand to the winding reel. These tworolls provide the front tension on the strip while the winding tensionis independent of the front tension.

Heretofore, the rolls of such pulling devices have been geared togetherand driven by a single motor. This method of operation has been foundunsatisfactory for the reason that small :7;

differences in the diameters of the rolls of the pulling device causeslippage and buckling of the strip on the rolls and sometimes cause one.of the rolls to carry most of the pulling load.

An object of the invention is to provide a 5 :control system for striptensioning rolls which .shall function to distribute the tensioning loadbetween the rolls in a predetermined adjustable proportion which shallmaintain the desired tension distribution between the tensioning rollsregardless of the speed of the mill, and which shall be simple andefiicient in operation, and inexpensive to manufacture, install,operate, and maintain.

These and other objects and advantages of the invention will be apparentfrom the following detailed description taken in connection with theaccompanying drawings in which:

Figure 1 is a diagrammatic view of a portion of a strip rolling millembodying the principal features of a preferred embodiment of theinvention, and r Fig. 2 is a diagrammatic view of a portion of a striprolling mill embodying the principal features of another embodiment ofthe invention.

In practicing the invention, tensioning rolls driven by separate motorsare positioned to en gage the strip between the winding reel, and a rollstand of a strip rolling mill. Substantially constant excitation isprovided for the tensioning roll motors and their relative excitationsare adjusted in accordance with the relative tensioning torques that itis desired to have the tensioning rolls exert upon the strip. Thearmatures oi the tensioning roll motors are connected in series circuitrelation and energized by the same source of adjustable voltage power asthe reel motor and the reducing roll stand motor. An auxiliary generatoris connected in series circuit relation with the tensioning roll motorsand is so controlled in accordance with armature current of thetensioning roll motors as to maintain the armature current substantiallyconstant. The constant armature current of the tensioning roll motorstogether with constant excitation of these motors results in theapplication of a substantially constant tension to the strip.

In the embodiment of Fig. 2 a tensiometer or tension responsive devicecontrols the excitation of the auxiliary generator to maintain thetorques of the tensioning roll motors substantially constant.

Referring to Figure l for a more detailed description of the invention,the tensioning rolls 2 and 4 driven by the motors 6 and 8, respectively,are positioned to subject the strip ID to tension as it extends orpasses from the rolls of the mill stand I2 to a reel M. The rolls of themill stand 12 and the reel 14 are driven by the motors I6 and 18,respectively.

The motors I6 and [B are supplied with power by a main generator 20which is continuously driven by any suitable means such as the motor 22.The generator 20 is connected to energize a power bus comprising theconductors 24 and 26. The armature of the roll stand motor I6 isconnected to the power bus by a circuit which extends from the conductor24 through the condoctor 28, the armature of the motor I6, and theconductor 30, to the conductor 26. The reel motor I is connected to thepower bus through a circuit which extends from the conductor 24 throughthe conductor 32, a controller, as indicated, and a conductor 34 to theconductor 26. The controller is merely indicated and not shown in detailfor the reason that any type of controller well known in the art whichwill function to control the reel motor l8 to maintain substantiallyconstant strip tension may be used. The speed of the motors l6 and I8 iscontrolled of the solenoid I00. Likewise, the energization of thecircuit of the field winding 96 will cause an impulse to be transmittedthrough the transformer IIO to the circuit of the solenoid I00. Thesecondary windings I24 and I28 of the transformers III! and I30,respectively, are so connected that the impulses transmittedtherethrough by changes of excitation and output potential of thegenerator 80 will cause movement of the solenoid I in the oppositedirection to that in which the solenoid I00 previously moved to causethe hereinbefore described changes of excitation and output potential ofthe generator 80. Thus, after the contact elements I46 and I48 haveclosed, the impulses transmitted through the transformers H0 and I30 tothe solenoid I00 will be such as to cause these contact elements to openand the contact elements I44 and I48 to close. The closure of contactelements I44 and I48 will act to energize the field winding 96 of thegenerator 80 in the opposite direction, which in turn, will cause thesolenoid I00 to move the arm I40 in the direction to open the contactelements I44 and I48 and to close the contact elements I46 and I48.Thus, the contact elements I44 and I46 will be continuously vibrated toexcite the generator 80, first in one direction, and then the other. Therelative lengths of the alternate periods of energization or" the fieldwinding 96 of the generator 60 will be controlled by the armaturecurrent of the motors 6 and 8 and the generator 80, which is the mainsource of energization of the winding of the solenoid I00, and itcontrols the average position of the arm I40, and, therefore, therelative length of the time of engagement of the contact element I44with the contact element I48 and the contact element I46 with thecontact element I48.

As the mill is started and brought up to speed by variation of theoutput potential of the main generator 20, the tension on the strip I0applied by the tensioning rolls 2 and 4 will remain constant because ofthe constant current regulating effect of the generator 60 in seriescircuit relation with the armatures of the motors 6 and 8, regardless ofthe value of the output potential of the generator 20.

It is usually desired to have a greater tension on the strip I0 betweenroll stand I2 and the tensioning roll 2 than between the reel I4 and thetensioning roll 4. The tensioning roll 2 will have a greater strippressure upon it, therefore, than the tension roll 4 and will be able tocarry a greater part of the tensioning load without slippage upon thestrip. To cause the tensioning roller 2 to carry a greater load than thetensioning roller 4, the relative excitations of the motors 6 and 8 maybe adjusted by the variable resistor 68 to provide the desired ratio ofmotor torques. These motor torques will be maintained throughout therange of operation of the mill since their armature currents aremaintained constant, and they have a constant field excitation.

The embodiment of the invention shown in Fig. 2 is substantially thesame as that of Fig. l with the exception that the regulator whichcontrols the excitation of the generator 80 is made responsive to atension responsive device I19 and constant strip tension is maintainedin response to the tension responsive device rather than a currentresponsive device. Like reference characters designate similar oridentical elements of the two systems.

Referring to Fig. 2, a shunting circuit for the rangement 98 extendsfrom the junction I53 through the conductors I02, B, I64 and I66, thecontact element I48 which is mounted upon the movable arm I40 actuatedby the solenoid I00, contact element I44, and conductor I68 to thejunction I05. A similar shunting circuit for the resistor leg I52 of theWheatstone bridge arrangement 98 extends from the junction I53 throughthe conductors I 02, B, I64 and I66 to the contact element I48, thecontact element I46, and the conductors I10 and I I8 to the junctionII9.

In this embodiment of the invention, the solenoid I00 is merely providedto vibrate the movable contact element I48 between the movable contactelements I44 and I46. The energizing circuit for the Winding of solenoidI00 extends from the conductor A through the conductor I12, the variableresistor I96, conductor H4, the secondary I28 of the transformer I30,conductor I26, the secondary winding I24 of the transformer II 0,conductor N6, the winding of the solenoid I00, and conductors I16, I66,and I64 to the conductor 13.

The engagement of contact element I48 with contact element I46 willclose the shunting circuit for the resistor leg I52 causing an unbalanceof the Wheatstone bridge 98. This will energize the field winding 96 ofthe auxiliary generator to change its output potential. The energizationof the field Winding 96 of the generator and the change of its outputpotential will cause impulses to be transmitted through the transformersH0 and I30 to the energizing circuit of the Winding of the solenoid I00in such a direction as to cause the contact element I48 to disengage thecontact element I46 and to engage contact element I44. This will causeenergization of the field winding 96 in the opposite direction whichwill result in movement of the contact element I48 out of engagementwith contact element I44 and into engagement with contact element I46.Thus, the contact element I48 will be made to vibrate continuously andcontinuous regulation is eilected eliminating hunting or excessivevariations of strip tension.

The positioning of the contact elements I44 and I46 with respect to thevibrating contact element I48 is controlled by the tension responsivedevice I19 which comprises a tensioning roller I80 mounted upon an armof a bell crank I82 in such position as to engage the strip I0 anddeflect it from its normal pass line, and a suitable actuating means,such as a fluid pressure operated piston and cylinder arrangement I84.The contact elements I44 and I46 may be actuated in accordance with themovement of the bell crank of the tension responsive device by means ofthe arm I86 attached thereto. The tension responsive device is soadjusted that variations in strip tension will vary the deflection ofthe strip and, therefore, the position of the contact elements I44 andI46 with respect to the vibrating contact element I48. Thus, therelative lengths of excitation of the generator 80 in one direction andthe other are controlled by the tension of the strip and automaticallyfunction to maintain a substantially constant strip tension.

It is to be understood that the application of the control system to arolling mill between the roll stand and a winding reel is merelyillustrative and that the system may be used equally well to control thetension between two roll stands of a tandem mill or between an unwindingreel and resistor leg I50 of the Wheatstone bridge ara roll stand. Inthe event that the system is used to control the back tension on thestrip between an unwinding reel and a roll stand, the dynamoelectricmachines 6, 8 and I8 would be operated as drag generators and the systemwould function to control the amount of braking torque applied to thestrip by these drag generators.

It is to be further understood that as many tensioning rolls and theirassociated dynamoelectric machines as desired may be provided, thesystem being applicable to several tensioning rolls in the same manneras it is applied to tWo tensioning rolls in the illustrated embodimentsof the invention.

It will be seen that I have provided a control system for a striptensioning device which shall function to distribute and maintain thedesired strip tension between a plurality of driven tensioning rollsregardless of the speed of the mill, which shall compensate for the I.R. drop in the dynamo-electric machines connected to the tensioningrolls, which shall be simple and efiicient in operation, and inexpensiveto manufacture, install, operate and maintain.

In compliance with the requirements of the patent statutes, I have shownand described herein the preferred embodiments of my invention. It is tobe understood, however, that the invention is not limited to the preciseconstructions shown and described, but is capable of modification by oneskilled in the art, the embodiments herein shown being merelyillustrative of the principles of my invention.

I claim as my invention:

1. In a strip tension control system for a pair of tensioning rolls overwhich the strip passes in travelling between a roll stand and a reel ofa strip rolling mill, in combination, a separate dynamo-electric machineconnected in driving relation with each of the tensioning rolls, meansconnecting the armatures of said dynamo-electric machines to a source ofpotential to which the roll stand and reel motors are connected andwhich is selectively variable to vary the speed of the mill, andauxiliary generator connected in series circuit relation with saiddynamo-electric machines, means providing selectively adjustablesubstantially constant excitations for said dynaom-electric machines,and means for so controlling the said auxiliary generator as to causesaid dynamo-electric machines to exert substantially constant torques onthe strip regardless of variations in the value of the potential of thesource of potential which energizes the reel and roll stand motors.

2. In a control system for a plurality of tensioning rollers over whicha strip of material passes in a partial wrap as it extends betweenadjacent work devices for controlling the tension on the strip ofmaterial as it passes between the work devices which are connected indriving relation with dynamo-electric machines whose armatures areenergized from a. power source of selectively adjustable potential, incombination, a separate dynamo-electrio machine connected in drivingrelation with each of the rollers, means connecting the armatures ofsaid roller dynamo-electric macl es the source of adjustable potentialto which the work device dynamo-electric machines are connected, meansproviding separately selectively adjustable sub stantially constantexcitations for said roller dynamo-electric machines, a generatorconnected in series circuit relation with said roller dynamoelectricmachines, and means for so controlling aasncca said generator as tocause said roller dynamoelectric machines to exert substantiallyconstant torques on the strip regardless of variations in the value ofthe potential of the power source.

3. In a control system for a plurality of tensioning rollers over whicha strip passes in a partial wrap as it extends between adjacent workdevices for controlling the tension on the strip as it passes betweenthe work devices which are connected in driving relation withdynamoelectric machines whose armatures are energized from a powersource oi selectively adjustable potential, the combination of aseparate dynamoelectric machine connected in driving relation with eachof the rollers, means connecting the armatures of said rollerdynamo-electric machines to the source of adjustable potential to whichthe work device dynamo-electric machines are connected, means forproviding and maintaining substantially constant ratios between theexcitations of the roller dynamo-electric machines, a generator, meansconnecting said generator armature in circuit with the armatures of saidroller dynamo-electric machines, and

. means for so controlling said generator as to cause said rollerdynamo-electric machines to exert substantially constant torques on thestrip regardless of variations in the potential of the power source.

4. In a control system for a plurality of tensioning rollers over whicha strip passes in a partial wrap as it extends between adjacent workdevices for controlling the tension on the strip as it passes betweenthe work devices which are connected in driving relation withdynamo-electric machines whose armatures are energized from a powersource of selectively adjustable potential, the combination of aseparate dynamoelectric machine connected in driving relation with eachof the rollers, means connecting the armatures of said rollerdynamo-electric ma chines to the source of adjustable potential to whichthe work device dynamo-electric machines are connected, means providingselectively adjustable substantially constant excitations for saidroller dynamo-electric machines, a generator, means connecting saidgenerator in circuit with said roller dynamo-electric machines, andmeans responsive to the armature current of said roller dynamo-electricmachines for so controlling said generator as to maintain substantiallyconstant current in the armatures of said roller dynamo-electricmachines regardless of variations of the potential of the said powerSOLH'CB.

5. In a control system for a plurality of tensioning rollers over whicha strip passes in a partial wrap as it extends between adjacent Workdevices for controlling the tension on the strip as it passes betweenthe work devices whichare connected in driving relation withdynamoelectric machines whose armatures are energized from a source ofselectively adjustable potential, the combination of a separatedynamo-electric machine connected in driving relation with each of therollers, means. connecting the armatures of said roller dynamo-electricmachines to the source of adjustable potential to which the work devicedynamo-electric machines are connected, :means providing selectivelyadjustable substantially constant excitations for said rollerdynamoei'e'ctric machines, a generator connected in cir- 'cuit with saidroller dynamo-electric machines, and means responsive to the striptension for .so controlling said generator as to maintain subelectricmachines, a generator, means connecting stantially constant tension onthe strip regardless of variations of the potential of the said powersource.

6. In a control system for a plurality of tensioning rollers over whicha strip passes in a partial wrap as it extends between adjacent workdevices for controlling the tension on the strip as it passes betweenthe adjacent work devices which are connected in driving relation withdynamo-electric machines whose armatures are energized from a powersource of selectively adjustable potential, the combination of aseparate dynamo-electric machine connected in driving relation with eachof the rollers, means connecting the armatures of said rollerdynamo-electric machines to the source of adjustable potential to whichthe work device dynamo-electric machines are connected, means forproviding and maintaining substantially constant ratios between theexcitations of the roller dynamo-electric machines, a generator,compensating means providing an excitation for said generatorproportional to the armature currents of said roller dynamo-electricmachines, means connecting said generator armature in circuit with thearmature of said roller dynamo-electric machines, and means for socontrolling said generator as to cause said roller dynamo-electricmachines to exert substantially constant torques on the strip regardlessof variations in the potential of the power source.

7. In a control system for a plurality of tensioning rollers over whicha strip passes in a partial wrap as it extends between adjacent workdevices for controlling the tension on the strip as it passes betweenthe work devices which are connected in driving relation withdynamoelectric machines whose armatures are energized from a powersource of selectively adjustable potential, the combination of aseparate dynamoelectric machine connected in driving relation with eachof the rollers, means connecting the armatures of said rollerdynamo-electric machines to the source of adjustable potential to whichthe work device dynamo-electric machines are connected, means providingselectively adjustable substantially constant excitations for saidroller dynamo-electric machines, a generator, means connecting saidgenerator in circuit with said roller dynamo-electric machines,compensating means providing an excitation for said generatorproportional to the armature currents of said roller dynamo-electricmachines, and means responsive to the armature current of said rollerdynamo-electric machines for so controlling said generator as tomaintain substantially constant current in the armatures of said rollerdynamo-electric machines regardless of variations of the potential ofthe said power source.

8. In a control system for a plurality of tensioning rollers over whicha strip passes in a partial wrap as it extends between adjacent workdevices for controlling the tension on the strip as it passes betweenthe work devices which are connected in driving relation withdynamoelectric machines whose armatures are energized from a source ofselectively adjustable potential, the combination of a separatedynamo-electric machine connected in driving relation with each of therollers, means connecting the armatures of said roller dynamo-electricmachines to the source of adjustable potential to which the work devicedynamo-electric machines are connected, means providing selectivelyadjustable substantially constant excitations for said roller dynamosaidgenerator in circuit with said roller dynamoelectric machines,compensating means providing an excitation for said generatorproportional to the armature currents of said roller dynamoelectricmachines, and means responsive to the strip tension for so controllingsaid generator as to maintain substantially constant tension on thestrip regardless of variations of the potential of the said powersource.

9. In a control system for a pair of tensioning rollers over which astrip of material passes in a partial wrap as it passes between arolling mill and a winding reel for controlling the tension on the stripof material as it is delivered from the rolling mill and wound onto thewinding reel which mill and reel are connected in driving relation withmotors whose armatures are energized from a power source of selectivelyadjustable potential, the combination of a separate drive motor for eachof the rollers, means connecting the armatures of said roller motors tothe power source to which the mill and reel motors are connected, meansproviding selectively adjustable substantially constant excitations forsaid roller motors, a generator, means connecting said generator incircuit with said roller motors, and means for so controlling saidgenerator as to cause said roller motors to exert substantially constanttorques on the strip regardless of variations in the potential of thepower source.

10. In a control system for a pair of rollers over which a strip ofmaterial passes in a partial wrap as it passes from an unwinding reel toa rolling mill for controlling the tension on the strip of material asit is fed to the rolling mill from the unwinding reel which mill andreel are connected in driving relation with a drive motor and a draggenerator, respectively, which drive motor and drag generator areconnected to a power source of selectively adjustable potential, thecombination of a separate drag generator driven by each of the rollers,means connecting the armatures of said roller drag generators to thepower source to which the reel drag generator and the mill motor areconnected, means providing selectively adjustable substantially constantexcitations for said roller drag generators, an auxiliary generator,means connecting said auxiliary generator in circuit with said rollerdrag generators, and means for so controlling said auxiliary generatoras to cause said roller drag generators to exert substantially constanttorques on the strip regardless of variations in the potential of thepower source.

11. In a system for controlling the tension on a strip of material as itis delivered from a rolling mill and wound onto a winding reel whichmill and reel are connected in driving relation with motors whosearmatures are energized from a power source of selectively adjustablepotential, the combination of a pair of rollers over which the strippasses in a partial wrap as it passes from the mill to the reel, aseparate drive motor for each of said rollers, means connecting thearmatures of said roller motors to the power source to which the milland reel motors are connected, means providing selectively adjustablesubstantially constant excitations for said roller motors, a generator,means connecting said generator in circuit with said roller motors, andmeans responsive to the strip tension for so controlling said generatoras to maintain substantially constant tension on the strip regardless ofvariations of the potential of the said powersource.

12. In a system for controlling the tension on a strip of material as itis delivered from a rolling mill and wound onto a winding reel whichmill and reel are connected in driving relation with motors whosearmatures are energized from a power source of selectively adjustablepotential, the combination of a pair of rollers over which the strippasses in a partial wrap as it passes from the mill to the reel, aseparate drive motor for each of said rollers, means connecting thearmatures of said roller motors to the power source to which the milland reel motors are connected, means providing selectively adjustablesubstantially constant excitations for said roller motors, a generator,means connecting said generator in circuit with said roller motors, andmeans responsive to the strip tension for so controlling said auxiliarygenerator as to maintain substantially constant tension on the stripregardless of variations of the potential of the said power source.

13. In a system for controlling the tension on a strip of material as itis delivered from a rolling mill and wound onto a winding reel whichmill and reel are connected in driving relation with motors whosearmatures are energized from a power source of selectively adjustablepotential, the combination of a pair of rollers over which the strippasses in a partial wrap as it passes from the mill to the reel, aseparate drive motor for each of said rollers, means connecting thearmatures of said roller motors to the power source to which the milland reel motors are connected, means providing selectively adjustablesubstantially constant excitations for said roller motors, a generator,means connecting said generator in circuit with said roller motors, andmeans responsive to the armature current of said roller motors for socontrolling said generator as to maintain substantially constant currentin the armatures of said roller motors regardless of variations of thepotential of the said power source.

WILLARD G. COCK.

